The present invention relates to a lens system within a camera, such as a video camera, with an automatically adjustable iris which is automatically varied in size in response to the light passing through the iris.
The present invention is primarily concerned with automatic adjustment of the iris of video cameras utilized during a scanning operation such as when used for surveillance purposes. During such operation, over the period of a day, different light conditions necessitate readjustment of the iris independence upon varying light conditions within the area under surveillance. Numerous types of systems have been developed for automatically adjusting the iris continuously throughout the operation of the video camera.
Exemplary of the types of systems used for automatically adjusting the iris of a video camera are those systems disclosed in the following U.S. Pat. Nos.: 2,885,471 to King; 2,898,536 to Musolf; 3,426,662 to Sevin; 3,496,289 to Tanner; 3,558,819 to LaRue; 3,767,853 to Bendel et al.; 4,037,254 to Monahan; 4,158,859 to Kerbel; 4,190,864 to Dischert; 4,268,866 to Rodgers; and, 4,300,167 to Miller et al. All of the systems disclosed by these patents provide the same basic type of operation of measuring the light passing through the iris, comparing such light to a predetermined standard and continuously providing a feedback signal for varying the size of the iris in response to the difference between the light passing through the iris and the predetermined standard.
During numerous types of operations of a video camera. The continuous operation of the drive motor for readjusting the size of the iris leads to frequent burn out of the drive motor. Since the motor control is normally built into the lens section of the camera, this results in the entire lens section needing to be removed and replaced which results in both a breakdown in the system and a costly expense.